A Case of Omental Abscess due to a Silent Fish Bone Perforation

76-year-old man admitted for lower acute abdominal pain showed signs of peritonitis irritation in the lower abdomen on admission. Blood laboratory data showed a C-reactive protein count of 5.0mg/dl. Endoscopy showed no abnormal findings. Ultrasonography and computed tomography showed a mildly enhanced 3.5cm mass suggesting inflammation of the fat tissue. We could not make a definitive diagnosis and conducted surgical resection under a tentative diagnosis of peritonitis due to perforation. At laparotomy, we found an abscess in the greater omentum 3×3.5 cm in diameter, free from other organs. The ruptured abscess had caused panperitonitis. There was no evidence of perforation in the gastric or intestinal wall, and no other intraabdominal abnormalities were found. We resected the mass and drained the abdominal cavity. Streptococcus intermedium was isolated from pus from the abscess. Microscopically, segmented spicules suspected of being of fish bone origin appeared in the omental abscess. Such a case of omental abscess due to perforation by a fish bone is very uncommon.